Method for producing long fiber reinforced thermoplastic resin pellets

ABSTRACT

Disclosed is a method for producing long-fiber-reinforced thermoplastic resin pellets, comprising, pultruding a plurality of reinforced fiber bundles in a molten thermoplastic resin while twisting the plurality reinforced fiber bundles to form a strand in which the reinforced fibers are coated with the thermoplastic resin, and cutting the strand to a predetermined length to form pellets, wherein the strand is pultruded under the conditions that the melt viscosity of the thermoplastic resin is adjusted such that the melt flow rate is 500 to 1500 g/10 min, and the twisting angle θ of the reinforced fiber bundles with respect to the pultruding direction of the strand is set as follows: 0°&lt;θ&lt;50°. As a result of this configuration, according to the method for producing long-fiber-reinforced thermoplastic resin pellets, pellets in which reinforced fibers are easily untwisted when the pellets are melted so that the reinforced fibers can be uniformly dispersed in molded articles can be produced with high productivity.

TECHNICAL FIELD

The present invention relates to a method for producing long fiberreinforced thermoplastic resin pellets.

BACKGROUND ART

A fiber reinforced thermoplastic resin (FRTP) is light and excellent instrength, and thus often used in an exterior of a vehicle, a vessel, andthe like. Among the fiber reinforced thermoplastic resin, particularly along fiber reinforced thermoplastic resin (LFRTP) containing reinforcedfibers whose fiber length is long is excellent in shock resistance andrigidity, and thus frequently used in a bumper and a body of anautomobile in recent years.

A molded article of such a long fiber reinforced thermoplastic resin isproduced from a resin material formed by melting pellets, and thereinforced fibers whose fiber length is long are dispersed anddistributed in the pellets. For example, Patent Document 1 discloses amethod for producing pellets, including pultruding a plurality ofreinforced fiber bundles such as glass rovings impregnated in a moltenthermoplastic resin bath from the thermoplastic resin bath whiletwisting the reinforced fiber bundles to form a strand in whichreinforced fibers are coated with a thermoplastic resin, and cutting thestrand to a predetermined length to obtain the pellets.

In this method for producing the pellets, a pair of take-up rolls isarranged on the downstream side of the thermoplastic resin bath, andthese rolls are arranged so as to be inclined in the directionsdifferent from each other with respect to the pultruding direction ofthe strand. Therefore, in the method for producing the pellets of PatentDocument 1, by nipping the reinforced fiber bundles between these rolls,the strand in which the reinforced fiber bundles are twisted is producedas an intermediate body.

In the strand serving as the intermediate body pultruded in such a way,the reinforced fiber bundles are firmly tightened to each other due totwisting, and the reinforced fiber bundles are gathered on the centerside of the strand. The reinforced fibers on the center side are coatedwith the thermoplastic resin so as to be surrounded. Therefore, when thestrand is pultruded from a die, the thermoplastic resin plays a role oflubrication and helps pultruding of the strand, and the reinforcedfibers are not brought into contact with the die and do not serve asresistance against the pultruding of the strand. As a result, the strandcan be pultruded with smaller force than a conventional method forproducing in which reinforced fiber bundles are pultruded in parallel.Since the resistance against the pultruding of the strand is small,there is an advantage that production speed of the pellets can beincreased.

In the method of producing of Patent Document 1 in which production isperformed with twisting, the reinforced fiber bundles are tightened dueto the twisting, so that a volume thereof is reduced. Thus, there isalso an advantage that a contained amount of the reinforced fibers canbe easily increased, and hence a content rate of the reinforced fiberscan be increased in comparison to the conventional method for producingin which the reinforced fibers are pultruded in parallel.

CITATION LIST Patent Document

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2008-221574

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, there is a tendency that the more melt viscosity of thethermoplastic resin coated over surfaces of the reinforced fibers islowered, the less the thermoplastic resin penetrates an interior of thetwisted reinforced fiber bundles. Therefore, when the thermoplasticresin having low melt viscosity is used, a part which is not impregnatedwith the thermoplastic resin is easily left in the interior of thereinforced fiber bundles. Thus, the part which is not impregnated withthe thermoplastic resin is left in an interior of the strand or thepellets after cooling as a clearance. When the pellets are melted,bubbles are easily generated in a master batch. As a result, when thethermoplastic resin having low melt viscosity is used, there is aproblem that a defect in an outer appearance is easily caused in themolded article.

In the method in which the reinforced fiber bundles are twisted, whenpultruding speed of the strand is increased, the reinforced fibers aresometimes firmly tightened in the interior of the strand. Such firmlytightened reinforced fibers are not easily untwisted even when thepellets are melted. Thus, there is also a problem that the reinforcedfibers are not properly dispersed in the molded article, and hence amechanical property of the molded article is deteriorated.

The present invention is achieved in consideration of the aboveproblems, and an object thereof is to provide a method for producinglong fiber reinforced thermoplastic resin pellets, the method beingcapable of producing the pellets containing reinforced fibers at a highcontent rate with high productivity, and also capable of easilyuntwisting the reinforced fibers at the time of melting the pellets touniformly disperse the reinforced fibers in a molded article withoutdeteriorating a mechanical property and an outer appearance of themolded article.

Means for Solving the Problems

In order to achieve the above object, the present invention has thefollowing technical means.

That is, a method for producing long fiber reinforced thermoplasticresin pellets of the present invention is a method for producing longfiber reinforced thermoplastic resin pellets, including pultruding aplurality of reinforced fiber bundles impregnated in a moltenthermoplastic resin bath from the thermoplastic resin bath whiletwisting the reinforced fiber bundles to form a strand in whichreinforced fibers are coated with the thermoplastic resin, and cuttingthe strand to a predetermined length to obtain the pellets, wherein thestrand is pultruded under conditions that the a melt flow rate ofthermoplastic resin is adjusted to 500 to 1,500 g/10 min, and a twistingangle θ of the reinforced fiber bundles with respect to the pultrudingdirection of the strand is set to 0°<θ<50°.

It should be noted that a long fiber reinforced thermoplastic resin is alonger resin among the reinforced fibers, in a case of the presentinvention, indicating that the thermoplastic resin is reinforced withusing the reinforced fibers having a fiber length of 3 to 25 mm.

The inventors assumed that even with using the thermoplastic resinhaving a low melt flow rate (melt viscosity) of 500 to 1,500 g/10 minwith which the thermoplastic resin does not easily sufficientlypenetrate an interior of the reinforced fiber bundles, when the twistingangle at the time of twisting the reinforced fiber bundles is adjusted,the reinforced fibers are not firmly converged. The inventors found thatby twisting the reinforced fiber bundles such that the twisting angle θis set to 0°<θ<50°, the pellets containing the reinforced fibers at ahigh content rate can be produced with high productivity withoutdeteriorating a mechanical property and an outer appearance of a moldedarticle, and completed the present invention.

According to the method as described above, the pellets containing thereinforced fibers at a high content rate such as pellets containing 50to 90 wt % of the reinforced fibers can be easily produced. The strandcan be pultruded at high production speed of 60 to 80 m/min with respectto the pultruding direction.

It should be noted that preferably, the thermoplastic resin is apolypropylene resin, and the reinforced fiber bundles are glass rovings.

Effects of the Invention

According to the method for producing the long fiber reinforcedthermoplastic resin pellets of the present invention, although thepellets containing the reinforced fibers at a high content rate can beproduced with high productivity, and the reinforced fibers can be alsoeasily untwisted at the time of melting the pellets to uniformlydisperse the reinforced fibers in the molded article, and the mechanicalproperty and the outer appearance of the molded article are notdeteriorated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A perspective view of a production device used in a method forproducing of the present invention.

FIG. 2 An enlarged plan view of a take-up device.

FIG. 3 Front views and sectional views of a strand in a case where atwisting angle is changed.

FIG. 4 A correlation diagram of a melt flow rate and the twisting angleof reinforced fibers.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a method for producing long fiber reinforced thermoplasticresin pellets 1 according to the present invention will be described indetail based on the drawings. Firstly, a pellet production device 2 usedin the method for producing of the long fiber reinforced thermoplasticresin pellets 1 will be described.

As shown in FIG. 1, the pellet production device 2 is provided with aplurality of coils 4 formed by winding reinforced fiber bundles 3, amixer/extruder 6 for mixing and melting a thermoplastic resin serving asa material (hereinafter, referred to as the resin 5), and a resinimpregnation head 7 for coating the reinforced fiber bundles 3 fed outfrom the coils 4 with the resin 5 plasticized by the mixer/extruder 6.The pellet production device 2 is also provided with a cooling device 9for cooling the reinforced fiber bundles 3 (a strand 8) coated with theresin 5 in the resin impregnation head 7, a take-up device 10 arrangedon the downstream side of the cooling device 9 for taking up the strand8, and a cutter 11 for cutting the cooled strand 8 to a predeterminedlength.

The coils 4 are formed by winding wires of the reinforced fiber bundles3. As reinforced fibers, an organic synthetic resin such as glass fiber,carbon fiber, and aramid, or metal fibers such as steel wires can beused. In the present embodiment, glass rovings 12 are used as thereinforced fiber bundles 3. The glass rovings 12 are formed by gatheringa plurality of glass monofilaments having a diameter of 4 to 30 μm suchthat a roving count is 1,000 to 4,000 tex and winding the glassmonofilaments into a cylindrical shape. Three glass rovings 12 areprovided in the present embodiment.

In the mixer/extruder 6, a screw shaft (not shown) provided with mixingblades is rotatably provided in a chamber 13 whose interior is hollow,and a material of the resin 5 loaded from a hopper 14 is melted andplasticized. The plasticized resin 5 is fed to the resin impregnationhead 7.

An example of the resin 5 supplied to the mixer/extruder 6 (the resin 5coated over the reinforced fibers) includes a polyolefin resin such aspolypropylene and polyethylene, a polyester resin such as polyethyleneterephthalate and polybutylene terephthalate, a polyamide resin such asnylon, a polycarbonate resin, polyacetal, or a thermoplastic resin suchas polyphenylene sulfide. In the present embodiment, a polypropyleneresin is used.

A silane coupling agent (an adhesiveness improver for the reinforcedfibers), a reactive diluent (an additive for improving a mechanicalproperty of the pellets such as shock resistance), an antioxidant, aultraviolet absorber, a light stabilizer, a flame retardant, a filler, acoloring pigment, or the like can be appropriately added to the resin 5.

The resin impregnation head 7 is formed into a cylindrical shape aboutan axis along the up and down direction, and the resin 5 plasticized bythe mixer/extruder 6 is stored in a hollow interior thereof. An upperend of the resin impregnation head 7 is opened upward, and thereinforced fiber bundles 3 can be drawn into the stored resin 5 fromthis opening. In the interior of the resin impregnation head 7, aplurality of (five in the present embodiment) impregnation rolls (notshown) is provided at intervals in the up and down direction, and astructure is that the reinforced fiber bundles 3 drawn from the openingof the upper end are untwisted while successively passing through theseimpregnation rolls and the plasticized resin 5 is impregnated into theinterior. On the lower end side of the resin impregnation head 7, anoutlet 16 for pultruding the reinforced fiber bundles 3 impregnated withthe resin 5 to an exterior is formed. A die 17 for shaping the resin 5over the reinforced fibers to form the strand 8 is provided in thisoutlet 16.

The cooling device 9 is to cool the strand 8 pultruded from the resinimpregnation head 7, arranged on the downstream side of the resinimpregnation head 7. The cooling device 9 is a water tank, in aninterior of which cooling water 18 is stored, capable of guiding andcooling the plasticized resin 5 coated over a surface of the strand 8into the cooling water 18. The strand 8 cooled in the cooling device 9is fed to the take-up device 10.

The take-up device 10 has a pair of upper and lower take-up rolls 19U,19D in contact with each other on outer peripheral surfaces. The pair ofupper and lower take-up rolls 19U, 19D is rotated in the rotationdirections different from each other to nip and feed out the strand 8 tothe downstream side.

As shown in FIG. 2, the pair of upper and lower take-up rolls 19U, 19Dis arranged so as to be inclined with respect to the pultrudingdirection of the strand 8, and the upper and lower take-up rolls 19U,19D are placed in the directions different from each other at an equalangle to each other. That is, in a case where the upper take-up roll 19Uis inclined anticlockwise with respect to the pultruding direction whenseen from the upper side by an inclination angle θ, the lower take-uproll 19D is inclined clockwise with respect to the pultruding directionby the inclination angle θ. Therefore, when the strand 8 is nippedbetween the take-up rolls 19, force in the twisting direction about anaxis is added to the strand 8, so that the strand 8 is twisted by atwisting angle θ corresponding to the inclination angle θ of the take-uprolls 19.

Since the entire strand 8 on the downstream side of the lowestimpregnation roll arranged in the interior of the resin impregnationhead 7 is twisted by the take-up rolls 19, the reinforced fiber bundles3 passing through the lowest impregnation roll are also twisted untilpassing through the die 17. As a result, in the strand 8 pultruded fromthe die 17, the reinforced fibers twisted in the resin impregnation head7 are coated with the thermoplastic resin 5.

The cutter 11 is arranged on the downstream side of the take-up device10, so as to cut the strand 8 cooled in the cooling device 9 to apredetermined length (for example, 3 to 10 mm). The cutter 11 isprovided with a plurality of blade portions 21 inclined with respect tothe direction of tangent at predetermined intervals in thecircumferential direction on an outer peripheral surface of acylindrical main body 20 rotated about an axis. Therefore, when thecutter 11 is rotated while abutting the strand 8 with the blade portions21, the strand 8 is cut by the cutter 11 to a predetermined length inaccordance with the intervals of the blade portions 21.

The pellets 1 obtained in such a way are melted before injection moldingand appropriately diluted by the diluting resin 5 when necessary, so asto be used as a master batch for injection molding.

The method for producing of the present invention is characterized bypultruding the strand 8 under conditions that melt viscosity of theresin 5 is adjusted such that a melt flow rate is 500 to 1,500 g/10 min,and the twisting angle θ of the reinforced fiber bundles 3 with respectto the pultruding direction of the strand 8 is set to 0°<θ<50°.

The melt flow rate (the melt viscosity of the resin 5) is an indicatorshowing a flow property of the plasticized resin 5, regulated by JISK7210 (a melt mass-flow rate of plastics-thermoplastics).

In the method for producing of the present invention, the resin 5 isadjusted such that the melt flow rate is 500 to 1,500 g/10 min. When themelt flow rate is less than 500 g/10 min, the flow property of the resin5 is deteriorated, so that the resin 5 does not easily penetrate aninterior of the reinforced fiber bundles 3. Meanwhile, when the meltflow rate exceeds 1,500 g/10 min, the viscosity of the resin 5 is toolow, so that the resin 5 is not easily attached to (coated over) thereinforced fibers.

This melt flow rate of the resin 5 is set to a high range as a value ofthe resin 5 used for the long fiber reinforced thermoplastic resinpellets 1, and a low range as the melt viscosity of the resin 5 coatedover surfaces of the reinforced fibers.

When the resin 5 having low melt viscosity is used in such a way, theresin does not easily sufficiently penetrate the interior of the twistedreinforced fiber bundles 3. Thus, the strand 8 is cooled while a partwhich is not impregnated with the resin 5 is left in the interior of thereinforced fiber bundles 3. As a result, the part which is notimpregnated with the resin 5 is left in an interior of the pellets 1 asa clearance. Then, when the pellets 1 are melted, bubbles are easilygenerated in the molten resin 5, so that there is a problem that adefect in an outer appearance is easily caused in a molded article.

Thus, in the present invention, the strand 8 is pultruded not only underthe condition that the melt flow rate of the resin 5 is adjusted to 500to 1,500 g/10 min but also under the condition that the twisting angle θof the reinforced fiber bundles 3 with respect to the pultrudingdirection of the strand 8 is set to 0°<θ<50° as described above,preferably 10°<θ<40°.

The twisting angle θ of the reinforced fiber bundles 3 with respect tothe pultruding direction of the strand 8 is adjusted in such a way forthe following reason.

That is, when the twisting angle θ of the reinforced fiber bundles 3 is0° as shown in FIG. 3( c), the reinforced fibers are not twisted. Thus,the reinforced fibers are aligned in parallel along the pultrudingdirection of the strand 8. As a result, the reinforced fibers also existin the vicinity of the surface of the strand 8 as shown in a sectionalview of FIG. 3( f). Thus, when the strand 8 is pultruded from the die17, the reinforced fibers in the vicinity of the surface get stuck withthe die 17, so that pultruding resistance of the strand 8 is increased.As a result, when production speed of the pellets 1 is increased,fracture of the strand 8 is easily generated, so that the pellets cannotbe stably produced while increasing the production speed.

However, when the twisting angle θ of the reinforced fiber bundles 3 is0° to 50° as shown in FIG. 3( a), preferably 10° to 40°, the reinforcedfibers are twisted. Thus, the reinforced fibers are easily gathered inthe interior of the strand 8. As a result, as shown in FIG. 3( d), whenthe strand 8 is pultruded from the die 17, the resin 5 coated over thereinforced fiber bundles 3 plays a role of lubrication and helpspultruding of the strand 8. Thus, the pultruding resistance of thestrand 8 is decreased, so that the production speed of the pellets 1 canbe increased. Since the reinforced fibers are gathered in the interiorof the strand 8, the reinforced fibers are not easily abutted with thedie 17, so that the fracture of the strand 8 is not caused.

Meanwhile, when the twisting angle θ of the reinforced fiber bundles 3is more than 50° as shown in FIG. 3( b), the reinforced fibers arestrongly twisted. As a result, as shown in FIG. 3( e), the reinforcedfibers are strongly tightened and gathered in the interior of the strand8 in a firmly converged state. Thus, when the pellets 1 are melted, thereinforced fibers are not easily untwisted and dispersed from thepellets 1. As a result, the reinforced fibers are not properly dispersedin the molded article, and hence a mechanical property of the moldedarticle is lowered.

Therefore, when the twisting angle θ of the reinforced fiber bundles 3with respect to the pultruding direction of the strand 8 is 0°<θ<50°,preferably 10°<θ<40°, the reinforced fibers can be prevented from beingexcessively firmly tightened in the interior of the strand 8 whilemaintaining a lubrication effect of the resin 5 coated over thereinforced fibers. In such a way, when the pellets 1 are melted, thereinforced fibers can be favorably dispersed in the master batch. Evenwhen pultruding speed of the strand 8 is increased to 60 to 80 m/minwith respect to the pultruding direction, breakage of the strand 8 isnot caused, so that the pellets 1 can be stably produced.

Further, in the pellets 1 produced in such a way, the reinforced fibersare twisted so as to be gathered in the interior of the strand 8. Thus,more reinforced fibers can be distributed in the resin 5 in comparisonto a case where the reinforced fibers are not twisted. As a result, eventhe pellets 1 containing the reinforced fibers at a high content rate of50 to 90 wt % can be stably produced.

EXAMPLES

Next, the method for producing the long fiber reinforced thermoplasticresin pellets 1 of the present invention will be described with usingExamples and Comparative Examples.

Examples and Comparative Examples were implemented by evaluating thelong fiber reinforced thermoplastic resin pellets 1 produced as belowwith predetermined evaluation items.

Regarding production of the pellets 1, two to three coils 4 of the glassrovings 12 (roving count: 2,310 tex) formed by gathering monofilamentshaving a diameter of 17 μm (specific gravity: 2.5 g/cm³) are prepared,and the glass rovings 12 are supplied from these coils 4 to the resinimpregnation head 7. It should be noted that the pellets 1 having afiber content rate of 55 wt % are produced in a case of two coils 4, andthe pellets 1 having a fiber content rate of 69 wt % are produced in acase of three coils 4. The resin 5 plasticized in the mixer/extruder 6was supplied to the resin impregnation head 7. This resin 5 ispolypropylene (PP) having specific gravity of 0.9 g/cm³. Afterimpregnating the glass rovings 12 with the resin 5 of the resinimpregnation head 7, the strand 8 was pultruded from an opening of thedie 17 having an opening diameter of 3.0 mm at pultruding speed of 60 to80 m/min, so that the strand 8 having a diameter of 3.0 mm was obtained.Then, the strand 8 was cut to 5 mm, so that the pellets 1 were produced.

It should be noted that the pellets 1 of Examples are formed by coatingthe glass monofilaments twisted so as to have the twisting angle θ of0°, 10°, 40°, 50° with the resin 5 adjusted such that the melt flow rateis 500 g/10 min, 800 g/10 min, 1,500 g/10 min.

The pellets 1 of Comparative Examples are formed by using the resin 5adjusted such that the melt flow rate is 300 g/10 min and twisting so asto have the twisting angle θ of 15°, or using the resin 5 adjusted suchthat the melt flow rate is 800 g/10 min and twisting so as to have thetwisting angle θ of 5° or 60°.

The pellets 1 of Examples and Comparative Examples obtained as abovewere evaluated in accordance with the following evaluation items.

Operation stability: whether or not a stably continuous operation isable to be performed at the pultruding speed of 60 to 80 m/min wasdetermined based on whether or not there is fuzz generated upon theglass monofilaments in stuck with the die, slippage of the strand 8 inthe take-up device 10, or the breakage of the strand 8. Evaluationresults are indicated by three types of rating symbols of ◯, ×, and Δ.The symbol × indicates a case where the breakage of the strand 8 wasgenerated, the symbol Δ indicates a case where the fuzz was generated inthe die or the slippage of the strand 8 was generated in the take-updevice 10, and the symbol ◯ indicates other cases (a case where thestably continuous operation was able to be performed at predeterminedspeed).

Impregnation property of resin into reinforced fibers: the impregnationproperty was determined based on whether or not the glass monofilamentswhich are not impregnated with the resin 5 are detached from the pellets1. Evaluation results are indicated by two types of rating symbols of ◯and ×. The symbol × indicates a case where detachment of the glassmonofilaments which were not impregnated with the resin was confirmed,and the symbol ◯ indicates a case where the detachment was notconfirmed.

Outer appearance of molded article: the outer appearance was determinedbased on whether or not the still-converged glass monofilaments notbeing dispersed in the pellets 1 are confirmed. Evaluation results areindicated by two types of rating symbols of ◯ and ×. The symbol ×indicates a case where the still-converged glass monofilaments wereconfirmed in the pellets 1, and the symbol ◯ indicates a case where theglass monofilaments were not confirmed.

The evaluation results are shown in Table 1.

No. of roving (fiber Melt Strand Strand Resin impregnation Outer contentflow rate twisting pultruding Operation property into appearance ofrate) (g/10 min) angle (°) speed (m/min) stability reinforced fibersmolded article Ex. 1 3 (68) 500 10 80 ∘ ∘ ∘ Ex. 2 3 (68) 500 20 80 ∘ ∘ ∘Ex. 3 3 (68) 800 20 60 ∘ ∘ ∘ Ex. 4 3 (68) 1,500 50 60 ∘ ∘ ∘ Ex. 5 2 (55)1,500 20 80 ∘ ∘ ∘ Com. 3 (68) 300 15 80 Δ x x Ex. 1 Com. 3 (68) 800 5 40x x x Ex. 2 (breakage) Com. 3 (68) 800 60 80 ∘ ∘ x Ex. 3

Seeing the results of Table 1, in Comparative Example 1 in which theresin 5 adjusted such that the melt flow rate is 300 g/10 min which issmaller than 500 g/10 min was used, since the detachment of the glassmonofilaments which were not impregnated with the resin was confirmed,the “impregnation property of resin into reinforced fibers” is notfavorable. Since the still-converged glass monofilaments were confirmedin the pellets 1, it is found that the “outer appearance of moldedarticle” is also inferior.

In Comparative Example 2 in which although the resin 5 adjusted suchthat the melt flow rate is 800 g/10 min within a range of 500 to 1,500g/10 min was used, the glass rovings 12 having the strand twisting angleof 5° which is lower than 10° were coated, not only the “impregnationproperty of resin into reinforced fibers” and the “outer appearance ofmolded article” are not favorable but also the breakage of the strand 8was generated, so that the “operation stability” is also inferior.

Further, in Comparative Example 3 in which the glass rovings 12 havingthe strand twisting angle of 60° which exceeds 50° were coated, althoughthe “operation stability” and the “impregnation property of resin intoreinforced fibers” are favorable, the still-converged glassmonofilaments were confirmed in the pellets 1, so that the “outerappearance of molded article” is not favorable.

Relative to these Comparative Examples, in any of Examples 1 to 5 inwhich the glass rovings 12 twisted so as to have the twisting angle θ of10 to 50° were coated with the resin 5 adjusted such that the melt flowrate is 500 to 1,500 g/10 min, it is found that the “operationstability”, the “resin impregnation property into reinforced fibers”,and the “outer appearance of molded article” are favorable.

Therefore, as shown in FIG. 4, when the production is performed suchthat the melt flow rate is 500 to 1,500 g/10 min and the twisting angleθ is within a preferable range of 10 to 50°, it is determined that eventhe pellets containing the reinforced fibers at a high content rate suchas pellets containing 50 to 90 wt % of the reinforced fibers can bestably produced while uniformly dispersing the reinforced fibers in themolded article without deteriorating the mechanical property and theouter appearance of the molded article.

The present invention is not limited to the above embodiment but ashape, a structure, material, combination, or the like of each membercan be appropriately changed within a range not changing the essence ofthe invention.

In the above embodiment, the two or three glass rovings 12 areexemplified. However, the number of the glass rovings 12 may be one, orfour or more.

In the above embodiment, a polypropylene resin is exemplified as theresin 5. However, polyethylene, nylon, polyethylene terephthalate,polycarbonate, and the like can be used as the resin 5.

In the above embodiment, a case where the pellets 1 containing 50 to 90wt % of the reinforced fibers are produced and a case where the strand 8is pultruded at 80 to 100 m/min with respect to the pultruding directionare taken as examples. However, the method for producing of the presentinvention can also be used in a case where the pellets 1 only containingless than 50 wt % of the reinforced fibers are produced and a case wherethe strand 8 is pultruded at 80 m/min or less with respect to thepultruding direction.

The present invention is described in detail with reference to theparticular embodiment. However, it is obvious to those skilled in theart that various modifications and corrections can be added withoutdeparting from the spirit and the scope of the present invention.

The present application is based on the Japanese patent application(Japanese Patent Application No. 2009-217032) applied on Sep. 18, 2009,and contents thereof are included herein as a reference.

INDUSTRIAL APPLICABILITY

The long fiber reinforced thermoplastic resin pellets of the presentinvention can be utilized as for example a molding material of a bumperand a body of an automobile.

Explanation of Reference Numerals

-   1: Pellet (long fiber reinforced thermoplastic resin pellet)-   2: Pellet production device-   3: Reinforced fiber bundle-   4: Coil-   5: Thermoplastic resin (resin)-   6: Mixer/extruder-   7: Resin impregnation head-   8: Strand-   9: Cooling device-   10: Take-up device-   11: Cutter-   12: Glass roving-   13: Chamber-   14: Hopper-   16: Outlet-   17: Die-   18: Cooling water-   19U: Upper take-up roll-   19D: Lower take-up roll-   20: Main body-   21: Blade portion-   θ: Twisting angle of reinforced fiber bundle (inclination angle of    take-up roll)

1. A method for producing long fiber reinforced thermoplastic resinpellets, comprising: pultruding a plurality of reinforced fiber bundlesin a molten thermoplastic resin while twisting the reinforced fiberbundles to form a strand in which reinforced fibers are coated with thethermoplastic resin; and cutting the strand to a predetermined length toobtain the pellets, wherein the strand is pultruded under conditionsthat melt viscosity of the thermoplastic resin is adjusted such that amelt flow rate is 500 to 1,500 g/10 min, and a twisting angle θ of thereinforced fiber bundles with respect to the pultruding direction of thestrand is set to 0°<θ<50°.
 2. The method for producing the long fiberreinforced thermoplastic resin pellets according to claim 1, wherein 50to 90 wt % of the reinforced fibers is contained in the pellets.
 3. Themethod for producing the long fiber reinforced thermoplastic resinpellets according to claim 1, wherein the strand is pultruded by 60 to80 m/min with respect to the pultruding direction.
 4. The method forproducing the long fiber reinforced thermoplastic resin pelletsaccording to claim 1, wherein the thermoplastic resin is a polypropyleneresin, and the reinforced fiber bundles are glass rovings.
 5. The methodfor producing the long fiber reinforced thermoplastic resin pelletsaccording to claim 2, wherein the strand is pultruded by 60 to 80 m/minwith respect to the pultruding direction.
 6. The method for producingthe long fiber reinforced thermoplastic resin pellets according to claim2, wherein the thermoplastic resin is a polypropylene resin, and thereinforced fiber bundles are glass rovings.
 7. The method for producingthe long fiber reinforced thermoplastic resin pellets according to claim3, wherein the thermoplastic resin is a polypropylene resin, and thereinforced fiber bundles are glass rovings.
 8. The method for producingthe long fiber reinforced thermoplastic resin pellets according to claim5, wherein the thermoplastic resin is a polypropylene resin, and thereinforced fiber bundles are glass rovings.